The present invention relates to an injection control system of a flocculating agent for forming flocs by flocculating a suspended substance in a water purifying plant, sewage treatment plant, and industrial sewer treatment plant and, more particularly, to a system for highly accurately recognizing an image of flocs to thereby accurately control the injection thereof.
In the water purifying plant, a flocculating agent is added into the collected raw water, a suspended substance is flocculated, a coagulated matter (hereinafter, referred to as flocs) is formed, and these flocs are precipitated and removed. Practically speaking, after the flocculating agent was injected into the high speed admixture pool, the raw water is led into the floc forming pool and slowly stirred, thereby forming flocs. The raw water drains out of the floc forming pool ad is led into the precipitation pool. The flocs are precipitated in this pool to thereby remove the suspended substance. The particulates which were not precipitated in the precipitation pool are removed in the filter bed.
In execution of the water treatment as mentioned above, if no floc is formed in the floc forming pool, the filter bed will be sooner or later choked. It is known that an injection amount of the flocculating agent is controlled to preferably form flocs. Hitherto, as disclosed in JP-B 59-29281, for example, the injection amount of the flocculating agent is controlled on the basis of the turbidity of the raw water and the diameter and surface area of the suspended substance.
On the other hand, for example, as shown in JP-A-54-143296, a method whereby the shape and size of floc are monitored by the image processes has been proposed. Practically speaking, on the basis of the floc image photographed by an industrial camera or the like, the portion (pixel) which is brighter than a predetermined brightness (threshold value) is set to the "1" level and this portion is recognized as a floc. On the contrary, the portion (pixel) which is darker than the predetermined value is set to the "0" level and this portion is recognized as a matter other than the floc. In this manner, the floc image is binarized and image processed, thereby monitoring the floc forming situation.
In the case where the injection amount of the flocculating agent was merely controlled on the basis of the turbidity of the raw water and the diameter and surface area of the suspended substance as in the foregoing conventional technique, the formation of flocs is influenced by the temperature, turbidity, diameter, pH, alkalinity, and the like, so that the flocs cannot be always preferably formed. In other words, since the flocculating agent is injected without directly measuring the floc forming state, the floc formation cannot be always preferably maintained. On the other hand, the idea such that flocs are recognized as images is well known. However, nothing is known with respect to how to evaluate the state of the floc formation from the recognized floc image and how to control the injection amount of the flocculating agent in order to preferably form flocs. Therefore, it is difficult to desirably control the floc formation on the basis of the floc image recognized.
On the other hand, according to the conventional technique, the portion of the floc image which is brighter than the threshold value is regarded as a floc. On the contrary, the portion which is darker than the threshold value is regarded as a background. In this manner, the binarization is performed. In this case, although the bright floc can be binarized even if the threshold value is set to a high value, the dark floc is regarded as a background because its brightness is below the threshold value. On the contrary, when the threshold value is set to a low value, although the dark floc can be also binarized, the noise existing in the background is also binarized as a flock. In addition, when the threshold value is set to a low value, the background portion around the bright floc is regarded as a part of the floc. Thus, this floc is binarized larger than the actual size or separate flocs existing closely are binarized as one floc. As described above, the conventional technique has a problem such that the floc cannot be accurately binarized.